10.04.11 - Lecture 9. Multigenic inheritance of traits...

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Lecture 9. Multigenic inheritance of traits Readings: Chapt 6: pg 219-235
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Factors that cause deviation from normal monohybrid and dihybrid ratios: X-linkage lethal alleles codominance and incomplete dominance multiallelism epistasis genetic linkage environmental conditions epigenetics
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A1 / A1 A2 / A2 A1 / A2 × × × × Dominance, recessiveness, partial dominance, codominance
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Penetrance is the percentage of individuals that show at least some degree of expression of a mutant genotype. Retinoblastoma, the most malignant form of eye cancer, arises from a dominant mutation of one gene, but only 75% of people who carry the mutant allele develop the disease. Expressivity reflects the range of expression of a mutant genotype. For instance, one or both eyes may be affected in retinoblastoma. The same genotype does not always produce the same phenotype
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Temperature-sensitive mutation Siamese cats 3 wks old 11 wks old 5 months old
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Siamese and Burmese cats are temperature sensitive genotypes of tyrosinase different temperature sensitive (Ts) alleles of the tyrosinase enzyme melanin pheomelanin DOPAquinone DOPA Tyrosine tyrosinase tyrosinase
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Multifactorial Inheritance Most traits are controlled by multiple genes. M utations in two different genes can give the same phenotype Two genes affecting the same trait can show: Independence (“additivity”, no interaction) Redundancy Complementarity (mutual epistasis) Epistasis Suppression
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Concepts on gene/allele interactions 1.Interactions between alleles within loci and alleles between loci cause deviation from Mendelian ratios in crosses 2.Complementation allows mutations to be assigned to genes, redundant genes to be identified, and genetic pathways to be described. 3.Epistasis is a general term for interactions between genes in which the phenotype produced by one is influenced by the other. It is also a specific term for an interaction in which one mutant allele cancels the effect of alleles at other loci.
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9 distinct genotypes YYRR, YYRr(2), YYrr YyRR(2), YyRr(4), Yyrr(2) yyRR, yyRr(2), yyrr 4 distinct phenotypes ( 9:3:3:1 ) Y_R_ = yellow round ( 9 /16) yyR_ = green round ( 3 /16) Y_rr = yellow wrinkled ( 3/ 16) yyrr = green wrinkled ( 1 /16) Seed color and pea shape are two different traits. What if two genes affect the
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This note was uploaded on 01/19/2012 for the course BIOLOGY 305 taught by Professor Kumar during the Fall '11 term at University of Michigan.

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10.04.11 - Lecture 9. Multigenic inheritance of traits...

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